Experimental evolution with bacteria in complex environments

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Abstract

Experiments with microbes are a powerful tool for addressing general questions in
evolutionary ecology. Microbial evolution is also interesting in its own right, and often
clinically relevant. I have used experimental evolution of bacteria (Pseudomonas spp.) in
controlled laboratory environments to investigate the role of environmental
heterogeneity in the evolution of phenotypic diversity. Some of my results provide
insight on general processes, while others are specific to bacteria. (1) I have shown that
variation in resource supply affects the evolution of niche breadth in complex
environments containing a range of available resources, leading to a peak in phenotypic
diversity at intermediate levels. (2) I have found that resource availability also affects
selection against redundant phenotypic characters, which is strongest when resources are
scarce. (3) Using experiments with bacteria and their protozoan predators, I have found
that selection for predator resistance varies with resource supply during a model
adaptive radiation. (4) I have looked at the role of periodic bottlenecks in population size
in the evolution of antibiotic-resistant bacteria. My results highlight the importance of
biochemical constraints specific to different resistance mutations. (5) Finally, I have
shown that bacterial adaptation to novel carbon substrates affects different growth
parameters simultaneously, and that the same response is seen in environments that
maintain different levels of phenotypic diversity. These findings emphasize the role of
environmental heterogeneity in the evolution of phenotypic diversity, but also show how
ecological and genetic factors can constrain adaptation to a given niche within a
heterogeneous environment.